Method of controlling instrumentation depth in total joint arthroplasty

ABSTRACT

A method to guide in preparation of a bone relies on an instrument having a shaft with a working end and a stop member. The shaft is free to translate along an axis. Surgical planning data is registered to the bone to determine intra-operative coordinates of the desired axis and depth. The instrument holder is positioned by the bone so the stop member contacts the instrument holder to prevent translating beyond the desired depth. Alternatively, an arm is manipulated to align the instrument with the desired axis. The working end rests on the bone to define a linear separation to the desired depth. By proximally translating the instrument holder to contact the stop member and distally translating the instrument holder along the shaft, the stop member physically stops translating beyond the desired depth. A surgical system for performing the methods is provided; a reamer or impactor are also disclosed.

RELATED APPLICATIONS

This application claims priority benefit of U.S. Provisional ApplicationSer. No. 62/574,429 filed 19 Oct. 2017; the contents of which are herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to the field ofcomputer-assisted orthopedic surgery, and more particularly tocontrolling instrumentation depth when preparing a bone or implanting aprosthesis during total joint arthroplasty.

BACKGROUND OF THE INVENTION

In the field of orthopedics, total joint arthroplasty (TJR) involves thereplacement of a subject's joint with prosthetic components. Inparticular, total hip arthroplasty (THA) requires the implantation ofboth a femoral component and an acetabular component. Traditionally, asurgeon pre-operatively determines the position and orientation (POSE)of the components before the prosthesis is seated or implanted. Thesurgeon then uses manual instruments to prepare the bones to receive theimplants in the planned POSE. Unfortunately, this approach can beunpredictable as being subject to the skill of the particular surgeon.Therefore, to improve the implant procedures, computer-assisted surgicalsystems have become popular to prepare and implant the cup prosthesismore accurately.

One such surgical system for planning and executing a THA procedure isthe TSOLUTION ONE® Surgical System (THINK Surgical, Inc., Fremont,Calif.). The TSOLUTION ONE® includes a pre-operative planningworkstation for generating a surgical plan, and a robotic surgicaldevice to execute the pre-operative plan intra-operatively. Prior to theprocedure, the surgeon pre-operatively plans a desired POSE for thefemoral and cup prosthesis using three-dimensional (3-D) bone models ofthe patient's anatomy and computer-aid design (CAD) files of theprostheses. The plan is then transferred to the robotic device in theoperating room (OR). Intra-operatively, the cup procedure begins byfixating the robotic device to the anatomy with the use of pins that arescrewed into the bone of a patient. After the fixation step, the bone isregistered to the robotic device, which transforms the position of thebone and the coordinates of the surgical plan to the robotic coordinatesystem. The robotic device then positions and constrains a reamer, byway of physical guide attached to the electro-mechanical arm, in theplanned orientation to permit the surgeon to prepare the acetabulum.Following the preparation of the acetabulum, an impactor with the cupprosthesis is attached to the electro-mechanical arm. The arm guides andconstrains the impactor in the planned orientation while the surgeonapplies a series of impaction forces on the impactor to implant the cupprosthesis.

However, in conventional systems, the electro-mechanical arm only alignsand constrains the reamer and impactor along the planned orientation,and as a result, the reamer and impactor are free to translate alongthat planned orientation. As the reamer and impactor are free totranslate, the surgeon may unintentionally under-ream the cup, over-reamthe cup, implant the prosthesis too proud or too low, all of which mayresult in sub-optimal patient outcomes and decreased implant longevity.

Therefore, there is a need in the art for a system and method to provideguidance, feedback, and/or physical stops in the preparation of a boneor the implantation of a prosthesis to a desired depth with asemi-manual operated instrument.

SUMMARY OF THE INVENTION

A method to guide a user in preparing a bone of a subject to receive aprosthesis to a desired depth is provided. The method utilizes a roboticsurgical system having a manipulator arm, an instrument holder attachedto the manipulator arm, and surgical planning data designating a desiredaxis and depth to implant the prosthesis in the bone. An instrument isprovided having a shaft with a working end and a stop member proximal tothe working end. The shaft is assembled to the instrument holder betweenthe working end and the stop member such that the shaft is free totranslate along a longitudinal axis of the instrument relative to theinstrument holder. Surgical planning data is registered to the bone todetermine intra-operative coordinates of the desired axis and depth. Theinstrument holder is positioned at a position proximal to the bone suchthat the stop member contacts the instrument holder to prevent theinstrument from being translated beyond the desired depth.

A method to guide a user in preparing a bone of a subject to receive aprosthesis to a desired depth is provided. The method utilizes a roboticsurgical system having a manipulator arm, an instrument holder attachedto the manipulator arm, and surgical planning data designating a desiredaxis and depth to implant the prosthesis in the bone. An instrument isprovided having a shaft with a working end and a stop member proximal tothe working end. The shaft is assembled to the instrument holder betweenthe working end and the stop member such that the shaft is free totranslate along a longitudinal axis of the instrument relative to theinstrument holder. Surgical planning data is registered to the bone todetermine intra-operative coordinates of the desired axis and depth. Thearm is manipulated to the desired axis so the longitudinal axis of theinstrument aligns with the desired axis. The working end rests on anouter surface of the bone to define a linear separation between theworking end resting on a surface of the bone and the desired depth toimplant the prosthesis. By proximally translating the instrument holderto contact the stop member and distally translating the instrumentholder along the shaft by a distance corresponding the linearseparation, the stop member contacts the instrument holder to physicallystop the instrument from being translated beyond the desired depth.

A surgical system for performing the above methods includes a surgicalrobot, a workstation including a computer, user-peripherals, and amonitor for displaying the graphical user interface (GUI). The computerincludes a processor, non-transient storage memory, and other hardware,software, data and utilities to execute the method. The user peripheralsallow a user to interact with the GUI and include user inputs via atleast one of a keyboard, mouse, or a touchscreen capability on themonitor.

A reamer or impactor instrument for preparing a bone of a subject toreceive a prosthesis to a desired depth utilizing a robotic surgicalsystem includes a shaft having a working end and a stop member proximalto the working end. The shaft is adapted to attach to an instrumentholder of a surgical robot between the working end and the stop memberwhere the shaft is free to translate along a longitudinal axis of theinstrument relative to the instrument holder such that the stop memberwill contact the instrument holder to prevent the instrument from beingtranslated beyond the desired depth.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples illustrative of embodiments are described below with referenceto figures attached hereto. In the figures, identical structures,elements or parts that appear in more than one figure are generallylabeled with a same numeral in all the figures in which they appear.Dimensions of components and features shown in the figures are generallychosen for convenience and clarity of presentation and are notnecessarily shown to scale. The figures are listed below.

FIG. 1 depicts a surgical system for controlling instrumentation depthin the context of an operating room in accordance with embodiments ofthe invention;

FIGS. 2A and 2B depict detailed views of an instrument holder and aninstrument of the surgical system of FIG. 1 in accordance withembodiments of the invention, where FIG. 2A depicts a reamer having ahandle to act as a stop member, and FIG. 2B depicts a reamer having anadded stop member;

FIG. 3 depicts a three-dimensional virtual model of a pelvis;

FIG. 4 depicts an instrument holder supporting a reamer and positionedrelative to an acetabulum to control reaming depth in accordance withembodiments of the invention;

FIG. 5 depicts an instrument holder in contact with a stop member of theinstrument in accordance with embodiments of the invention;

FIG. 6 depicts a suppressing element associated with an instrumentholder in accordance with embodiments of the invention; and

FIG. 7 depicts a depth sensor associated with an instrument holder inaccordance with embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention has utility as a system and method for providingguidance, feedback, physical stops, or a combination thereof to preparea bone to a desired depth or implant a prosthesis to a desired depthwith a semi-manual operated instrument. The system and methods areparticularly useful in the preparation of the acetabular cup andimplantation of a cup prosthesis in total hip arthroplasty (THA) using asemi-manual operated reamer or impactor that are physically constrainedalong a planned orientation with a surgical robot. However, it should beappreciated that although the system and methods are described herein inthe context of cup preparation during THA, the system and methods mayalso apply to other orthopedic applications such as pedicle screwplacement during spine surgery, pin placement in bone fracturereconstruction, maxillofacial reconstruction, cranial surgery, ligamentreconstruction surgery, and other procedures requiring precision andaccuracy along a depth axis or plane (i.e., an axis or plane orientedinto the body). It is further appreciated, a miniaturized toolassociated with an inventive system is amenable to repair of metatarsal,metacarpal and otic bone structures that are currently difficult toaddress surgically.

The present invention will now be described with reference to thefollowing embodiments. As is apparent by these descriptions, thisinvention can be embodied in different forms and should not be construedas limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. For example, features illustrated with respect toone embodiment can be incorporated into other embodiments, and featuresillustrated with respect to a particular embodiment may be deleted fromthat embodiment. In addition, numerous variations and additions to theembodiments suggested herein will be apparent to those skilled in theart in light of the instant disclosure, which do not depart from theinstant invention. Hence, the following specification is intended toillustrate some particular embodiments of the invention, and not toexhaustively specify all permutations, combinations and variationsthereof.

It is to be understood that in instances where a range of values areprovided that the range is intended to encompass not only the end pointvalues of the range but also intermediate values of the range asexplicitly being included within the range and varying by the lastsignificant figure of the range. By way of example, a recited range offrom 1 to 4 is intended to include 1-2, 1-3, 2-4, 3-4, and 1-4.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The terminology used in thedescription of the invention herein is for the purpose of describingparticular embodiments only and is not intended to be limiting of theinvention.

All publications, patent applications, patents and other referencesmentioned herein are incorporated by reference in their entirety.

Unless indicated otherwise, explicitly or by context, the followingterms are used herein as set forth below.

As used in the description of the invention and the appended claims, thesingular forms “a,” “an” and “the” are intended to include the pluralforms as well, unless the context clearly indicates otherwise.

Also, as used herein, “and/or” refers to and encompasses any and allpossible combinations of one or more of the associated listed items, aswell as the lack of combinations when interpreted in the alternative(“or”).

As used herein, the term “semi-manual” in the context of an operationalinstrument refers to an instrument that is not fully automated tooperate. For example, a semi-manual operated reamer, or semi-manualoperated drill-bit, may be constrained in a planned orientation by anautonomous surgical robot where a user manually translates the reamer ordrill-bit along the planned orientation and drives the reamer ordrill-bit with a manually operated drill.

As used herein, the term “digitizer” refers to a measuring devicecapable of measuring physical coordinates in three-dimensional space.For example, the “digitizer” may be: a “mechanical digitizer” havingpassive links and joints, illustratively including the high-resolutionmechanical sensor arm described in U.S. Pat. No. 6,033,415; anon-mechanically tracked digitizer probe (e.g., optically tracked,electromagnetically tracked, acoustically tracked, and equivalentsthereof) as described in for example U.S. Pat. No. 7,043,961; or anend-effector of a surgical robot.

As used herein, the term “digitizing” refers to the collecting,measuring, and/or recording of physical points in space with adigitizer.

As used herein, the term “pre-operative bone data” refers to bone dataused to pre-operatively plan a procedure before making modifications tothe actual bone. The pre-operative bone data may include one or more ofthe following: a patient's actual exposed bone prior to modification; a2-D image data set of a bone; a 3-D virtual generic bone model; aphysical bone model; a 3-D virtual patient-specific bone model; a set ofdata collected directly on a bone intra-operatively commonly used withimageless computer-assist devices; or a combination thereof.

As used herein, the term “registration” refers to the determination ofthe POSE and/or coordinate transformation between two or more objects orcoordinate systems such as a computer-assisted device, a bone,pre-operative bone data, surgical planning data (i.e., an implant model,cut-file, virtual boundaries, virtual planes, or other tissuemodification instructions associated with or defined relative to thepre-operative bone data), and any external landmarks (e.g., a fiducialmarker array) associated with the bone, if such landmarks exist. Methodsof registration are well known in the art illustratively including themethods described in U.S. Pat. Nos. 6,033,415, 8,010,177, and 8,287,522.

As used herein, the term “translation” or “translating” refers to amovement that is only along an axis.

Embodiments of the present invention describe a system and methods forproviding guidance, feedback, and/or physical stops to aid a user inpreparing a bone or implanting a prosthesis to a desired depth with asemi-manual operated instrument. Examples of systems, and morespecifically robotic surgical systems that may be adapted or modifiedwith the inventive embodiments described herein include the TSolutionOne Surgical System (THINK Surgical, Inc., Fremont, Calif.) as generallydescribed in U.S. Pat. No. 5,086,401, the RIO Robotic Arm InteractiveOrthopedic System (Stryker-Mako, Fr. Lauderdale Fla.) as described inU.S. Pat. No. 8,010,180, the ROSA Surgical System (Zimmer-Biomet,Warsaw, Ind.) as described in U.S. Pat. No. 9,237,861, as well as otherserial-chain manipulators, parallel manipulators, hand-heldmanipulators, or master-slave robotic systems having autonomous,semi-autonomous, or haptic control.

Exemplary Surgical System

Referring now to the figures, FIG. 1 illustrates a specific inventiveembodiment of a robotic surgical system 100 for preparing a bone to adesired depth, or implanting a prosthesis to a desired depth. Thesurgical system 100 generally includes a surgical robot 102, a computingsystem 104, and may include at least one of a mechanical digitizer 122or a non-mechanical tracking system 108.

The surgical robot 102 in some embodiments includes a moveable base 110,a manipulator arm 112 connected to the base 110, and an end-effectorassembly 114 removably attached to a distal end of the manipulator arm112 by way of a flange or coupler 115. The base 110 may include anactuator to adjust the height of the surgical robot 102. The base 110may further include a set of wheels 116 to maneuver the base 110, whichmay be fixed into position using a braking mechanism such as a hydraulicbrake. The manipulator arm 112 includes various joints and links tomanipulate the end-effector assembly 114 in one or more degrees offreedom. The joints illustratively include prismatic, revolute,spherical, or a combination thereof. The end-effector assembly 114generally includes an instrument holder 118 for holding and/or operatingan instrument 120. The surgical robot 102 may further include amechanical digitizer 122 mounted to the base 110.

The computing system 104 generally includes a planning computer 124; adevice computer 126; a tracking computer 128 if a tracking system 108 ispresent; and peripheral devices. The planning computer 124, devicecomputer 126, and tracking computer 128, may be separate entities,single units, or combinations thereof depending on the surgical system.For example, the device computer 126 may execute all of the operationsfor the tracking system 108 that would otherwise be performed on atracking computer 128. The peripheral devices allow a user to interfacewith the surgical system components and may include: one or moregraphical user interfaces (GUI) displayed on a monitor (130 a, 130 b),and user-input mechanisms illustratively including a keyboard 132, mouse134, pendent 136, joystick 138, foot pedal 140, or the monitor 130 insome inventive embodiments has touchscreen capabilities.

The planning computer 124 contains hardware (e.g., processors,controllers, and/or memory), software, data, and utilities that are insome inventive embodiments dedicated to the planning of a surgicalprocedure, either pre-operatively or intra-operatively. This may includereading medical imaging data, segmenting imaging data, constructingthree-dimensional (3D) virtual models, storing computer-aided design(CAD) files, providing various functions or widgets to aid a user inplanning the surgical procedure, and generating surgical plan data. Thefinal surgical plan includes surgical planning data/instructions definedrelative to the pre-operational bone data to modify the bone. Theplanning data/instructions may include, for example: a set of cuttingparameters (e.g., points, vectors, velocities and accelerationinstructions) of a cut-file to autonomously modify a volume of bone; anaxis or plane to align an instrument to modify the bone coincident withthat axis or plane; a set of virtual boundaries to haptically constrainan instrument within those boundaries to modify the bone; a set of axes,planes, or drill holes to drill pins or screws into the bone; or agraphically navigated set of instructions to modify the bone. The datagenerated from the planning computer 124 may be transferred to thedevice computer 126 and/or tracking computer 128 through a wired orwireless connection in the operating room (OR); or transferred via anon-transient data storage medium (e.g., a compact disc (CD), a portableuniversal serial bus (USB) drive) if the planning computer 124 islocated outside the OR.

The device computer 126 in some inventive embodiments is housed in themoveable base 110 and contains hardware, software, data, and utilitiesthat are preferably dedicated to the operation of the surgical robot102. The device computer 126 may include surgical device control,robotic manipulator control, the processing of kinematic and inversekinematic data, the execution of registration algorithms, the executionof calibration routines, the execution of the surgical planning data,coordinate transformation processing, providing workflow instructions toa user, communicating with the mechanical digitizer 122 to collect andtransform points, and utilizing POSE data from the tracking system 108,if present.

The optional tracking system 108 of the surgical system 100 in someinventive embodiments include two or more optical receivers (138 a, 138b) to detect the position of fiducial markers (e.g., retroreflectivespheres, active light emitting diodes (LEDs)) uniquely arranged on rigidbodies. The fiducial markers arranged on a rigid body are collectivelyreferred to as a fiducial marker array 142, where each fiducial markerarray 140 has a unique arrangement of fiducial markers, or a uniquetransmitting wavelength/frequency if the markers are active LEDs todistinguish one marker array from another. An example of an opticaltracking system is described in U.S. Pat. No. 6,061,644. The trackingsystem 108 may be built into a surgical light, located on a boom, astand 144, or built into the walls or ceilings of the OR. The trackingsystem computer 128 may include tracking hardware, software, data andutilities to determine the POSE of objects (e.g., pelvis P, surgicalrobot 102) in a local or global coordinate frame. The POSE of theobjects is collectively referred to herein as POSE data, where this POSEdata may be communicated to the device computer 126 through a wired orwireless connection. Alternatively, the device computer 126 maydetermine the POSE data using the position of the fiducial markersdetected from the optical receivers (138 a, 138 b) directly.

The POSE data is determined using the position data detected from theoptical receivers (138 a, 138 b) and operations/processes such as imageprocessing, image filtering, triangulation algorithms, geometricrelationship processing, registration algorithms, calibrationalgorithms, and coordinate transformation processing. For example, thePOSE of a optically tracked digitizer probe 146 with an attached probefiducial marker array 142 c may be calibrated such that the probe tip iscontinuously known as described in U.S. Pat. No. 7,043,961. The POSE ofan instrument tip or instrument axis of the instrument 120 may be knownwith respect to a robot fiducial marker array 142 b using a calibrationmethod as described in U.S. Prov. Pat. App. 62/128,857. The robotfiducial marker array 142 b is depicted on the manipulator arm 112 butmay also be positioned on the base 110 or end-effector assembly 114.Registration algorithms may be executed to determine the POSE andcoordinate transforms between a bone (e.g., pelvis P), pre-operativebone data, a fiducial marker array 142 a, a surgical plan, a surgicalrobot 102, and/or tracking system 108 using the registration methods asdescribed above.

The POSE data from the tracking system 108 in some embodiments are usedby the computing system 104 during the procedure to update the bone andsurgical plan coordinate transforms relative to the end-effectorassembly 114 so the surgical robot 102 can accurately execute thesurgical plan in the event any bone motion occurs. It should beappreciated that in certain embodiments, other tracking systems to trackthe bone in real-time may be incorporated with the surgical system 100such as an electromagnetic field tracking system or the mechanicaldigitizer 122.

In a particular inventive embodiment, the surgical system 100 does notinclude a tracking system 108 or other sensors to track the bone inreal-time, but instead employs a bone fixation system to fix the bonedirectly to the surgical robot 102, a mechanical digitizer 122 fordigitizing, and a bone motion monitoring system to monitor bone motionbeyond a pre-determined amount during the procedure, such as the systemdescribed in U.S. Pat. No. 5,086,401.

With reference to FIGS. 2A and 2B, a particular inventive embodiment ofan end-effector assembly 114′ for controlling the depth of an instrument120′ is shown. The end-effector assembly 114′ generally includes aninstrument holder 118 and the instrument 120′ assembled to theinstrument holder 118. In the particular inventive embodiment shown inFIGS. 2A and 2B, the instrument shown generally as instrument 120 inFIG. 1 is a reamer 120′ (as illustrated throughout the figures) forpreparing the acetabular cup during THA. However, it should beappreciated that the instrument 120 may be a drill-bit for drillingbone, a pedicle screw for spinal surgery, a bone screw or pin for bonefractures, a broach for creating cavities, or other semi-manual operatedinstruments. The instrument 120′ generally includes a shaft 152 having aworking end 154, a stop member 156 proximal to the working end 154, anda longitudinal axis ‘L’. The working end 154 may either be: a) a tool toperform work on the bone illustratively including a grater 155 of areamer 120′, flutes of a drill bit; or b) a prosthesis to be implantedinto the bone, illustratively including a cup prosthesis or pediclescrew. The working end 154 further includes a tool center point 158 (orprosthesis center point) defined as the center and most distal portionof the working end 154. With reference to FIG. 2A, the stop member 156may be a handle 160 of the instrument 120′, the handle 160 having adistal stop end 162. In another embodiment, with reference to FIG. 2B,the stop member 156 is a body 164 having at least a portion of itsgeometry (e.g., diameter, or a protrusion) greater than the shaft 152.The body 164 is positioned between the handle 160, or a proximal end 166of the instrument 120″, and the working end 154 of the instrument. Thebody 164 may be adjustable along the length of the shaft 152, or fixedlyattached or integral to the shaft 152 at a specific position on theshaft 152. The body 164 likewise has a distal stop end 162.

The instrument holder 118 of FIG. 2A includes a mount 168 to couple tothe distal end of the manipulator arm 112 by way of a coupler 115, andan instrument assembly portion 170 for assembling the instrument 120′thereto. In a particular inventive embodiment, the instrument assemblyportion 170, with the aid of the manipulator arm 112, is configured tosupport and hold the instrument (120′, 120″) along a fixed axis (e.g.,anteversion/inclination axis for cup reaming, a desired axis for apedicle screw, the longitudinal axis ‘L’ of the instrument 120′), whilepermitting a user to at least one of: a manually translate theinstrument 120′ along the fixed axis (as shown by the arrow ‘T’); and/orb manually rotate the instrument 120′ about the fixed axis. Theinstrument assembly portion 170 may be a body having a receivingopening, a clasp, a latch, or a flange having fixation elements such asthreads, to receive the instrument (120′, 120″) thereon. In a particularembodiment, the instrument assembly portion 170 is a linear bearing thatreceives the instrument (120′, 120″) there through to permit manualtranslation and/or rotation of the instrument (120′, 120″). It is worthnoting, that the ‘manual rotation’ may be performed by a user's hands,or by a secondary device such as a manually operated drill. For example,a reamer 120′ may have a proximal end 166 configured to be received in adrill chuck of a drill, where a user may manually operate the drill to‘manually rotate’ a grater 155 of the reamer 120′. The instrumentassembly portion 170 further includes a proximal stop end 172 configuredto make contact with the distal stop end 162 of the stop member 156 torestrict linear motion of the instrument (120′, 120″) to aid in thecontrol of the depth of the instrument (120′, 120″), which is furtherdescribed in more detail below.

Surgical Planning

Generally, the user plans the POSE of a prosthesis model relative topre-operative bone data in a pre-operative planning software programhaving a graphical user interface (GUI). In a particular embodiment,with reference to FIG. 3, the pre-operative bone data is a virtualthree-dimensional (3-D) bone model, such as a 3-D pelvis model (PM),generated from an image data set of a subject's anatomy. The image dataset may be collected with an imaging modality such as computedtomography (CT), magnetic resonance imaging (MRI), X-ray scans,ultrasound, or a combination thereof. The 3-D bone model(s) are readilygenerated from the image data set using medical imaging software such asMimics® (Materialise, Plymouth, Mich.) or other techniques known in theart such as the one described in U.S. Pat. No. 5,951,475. A set of 3-Dcomputer aided designs (CAD) models of the manufacturer's prostheses(prostheses models) are pre-loaded in the software, such as a cupprosthesis model 200, that allows the user to place the components of adesired prosthesis to the 3-D bone model of the boney anatomy todesignate the best fit, position, orientation, and depth of theprosthesis to the bone. The user can then save this surgical planningdata to an electronic medium that is loaded and read by acomputer-assisted device to assist the surgeon intra-operatively toprepare the bone to receive the physical prosthesis according to theplan.

In a specific inventive embodiment, the user plans a desired depth, andaxis 204 (e.g., desired anteversion angle and inclination angle) of acup prosthesis model 200 relative to a patient-specific 3-D pelvis model(PM). As used herein, a ‘desired axis’, such as desired axis 204, refersto both the orientation of the axis and the position of the axisrelative to the anatomy. The cup prosthesis model 200, and correspondingcup prosthesis, includes an apex 202, defined as the deepest portion ofthe prosthesis that contacts the bone along a desired axis. It should beappreciated, that the apex of a pedicle screw for example, wouldcorrespond to the distal tip of the screw according to this definitionof ‘apex’. In other embodiments, the user plans the position for a cupprosthesis using other pre-operative data, such as a 2-D image data set,or a model of the bone generated intra-operatively from a cloud ofpoints collected directly on the exposed bone. In any case, the surgicalplanning data preferably includes at least a desired axis for theprosthesis, and the desired depth for the prosthesis. In a specificinventive embodiment, the desired depth for the prosthesis is defined bythe intersection of the apex 202 of the prosthesis with thepre-operative bone data. It is also appreciated, that a user maydesignate a depth for the prosthesis on the pre-operative bone datadirectly using software widgets or tools without the use of a prosthesismodel. The surgical planning data, with the desired axis and depth, isthen transferred, wired or wirelessly, to the device computer 126 and/ortracking computer 128 to prepare a bone and/or implant a prosthesisalong the desired axis and depth as further described below.

Intraoperative Depth Control

With reference to FIG. 1 and FIG. 4, an example of several methods forcontrolling the depth of an instrument during total joint arthroplastywith a robotic surgical system 100 is illustrated in the context ofacetabular cup preparation during total hip arthroplasty.Intraoperatively, the acetabulum of the pelvis (P) is exposed usingconventional incision techniques. In one inventive embodiment, atracking array 142 a is fixed to a portion of the pelvis (P) to trackany motion of the pelvis during the procedure with a tracking system108. In an alternative inventive embodiment, one or more fixation pinsare drilled into the pelvis and assembled to the surgical robot 102 witha series of fixation rods to rigidly fix the pelvis (P to the robot 102.Subsequently, at least two of the pelvis (P), pre-operative bone data,surgical planning data, and any landmarks associated with the pelvis (P)(e.g., tracking array 142 a), are registered to the surgical robot 102using the aforementioned registration techniques. If an imagelesscomputer-assist device is used, the user may collect several points inand around the acetabulum of the pelvis (P) to create a point cloudrepresentation of the acetabulum. During the point collection, the boneis inherently registered to the computer-assist device, where the usermay then plan the placement of the prosthesis relative to the pointcloud representation. The registration step provides the surgical system100 with the intraoperative coordinates for the desired axis 204 and thedesired depth 202 to implant the prosthesis in the acetabulum as definedin the surgical plan.

A reamer 120″, as described above, is assembled to the instrumentassembly portion 170 and autonomously manipulated, by way of themanipulator arm 112, such that the longitudinal axis ‘L’ of the reamer120′ aligns with the desired axis 204 defined in the plan. Preferably,the reamer 120′ is positioned proximal to the pelvis ‘P’ along thedesired axis 204 such that the reamer 120′ does not contact the anatomy.After the longitudinal axis ‘L’ of the reamer 120′ is aligned with thedesired axis 204, the reaming depth may be controlled by severaldifferent methods.

In a particular inventive embodiment of a method for controlling thedepth of the reamer 120″ with the axes ‘L’ and 204 aligned, the surgicalrobot 102 generally positions the instrument holder 118 at a positionproximal to the bone such that the stop member 156 will contact theinstrument holder 118 to prevent the reamer 120″ from being translatedbeyond the desired depth. More specifically, the length from the distalstop end 162 of the stop member 156 to the tool center point 158 isknown and stored in the computing system 104. The proximal stop end 172of the instrument assembly portion 170 is also known by programming thegeometry of the instrument holder 118 as a link in the kinematic chainof the manipulator arm 112. The surgical robot 102 also knows thecoordinates of the desired depth (i.e., the planned position of the apex202) in the robotic or tracking system coordinate frame from theregistration. Therefore, the surgical robot 102 can position theproximal stop end 172 of the instrument holder 118 at a distance D1 fromthe desired depth such that the distance D1 is equal to a distance D2,where the distance D2 corresponds to the known distance between thedistal stop end 162 of the stop member 156 and the tool center point158. As the user reams the acetabulum and translates the reamer 120″towards the desired depth, the distance between the distal stop end 162and proximal stop end 172 decreases. Once the user reaches the desireddepth, the proximal stop end 172 of the instrument holder 118 makescontact with the distal stop end 162 of the stop member 156, therebyphysically stopping the user from over-reaming the acetabulum. If theuser needs multiple reamers with graters 155 of increasing diameter,then the distance D2 of the distal stop member 162 relative to the toolcenter point 158 should be consistent from reamer to reamer; however,this consistent distance is not absolutely necessary if the userperforms a few additional steps as described below (e.g., digitizing thetool center point 158 and/or one or more points on the distal portion162 of the stop member 156). After reaming is complete, an impactor forimpacting a cup prosthesis into the acetabulum is assembled to theinstrument assembly portion 170 and the process is repeated to ensurethe cup prosthesis is implanted to the desired depth.

In another inventive embodiment of a method for controlling the depthwith the axes ‘L’ and 204 aligned, a user may first rest the grater 155on the outer edge of the acetabulum. The instrument holder 118 is thentranslated, manually or automatically, along the desired axis 204 in aproximal direction towards the stop member 156, with the grater 155still resting on the acetabulum, until the proximal stop end 172 makescontact with the distal stop end of the stop member 156. Theconfiguration of the proximal stop end 172 of the instrument assemblyportion 170 in contact with the distal stop end of handle 160 is shownin FIG. 5, where the stop member is a handle 160 of the reamer 120′.Next, a signal is sent to the computing system 104 to notify the systemof the contact. In one inventive embodiment, the user signals to thecomputing system 104, by way of a user input mechanism or signal to thetracking system, that the proximal stop end 172 of the instrumentassembly portion 170 and distal stop end distal stop end of handle 160are in contact. In another inventive embodiment, the stop member 156and/or instrument assembly portion 170 may include one or more contactsensor(s) (174 a, 174 b) to automatically communicate the contact to thecomputing system 104.

Next, a length of a margin is determined, the margin being the distancebetween the current position of the tool center point 158 resting on theouter edge of the acetabulum and the desired depth (the planned positionof the apex 202). The length of the margin may be determined duringsurgical planning by defining a circle to represent the outer edge ofthe acetabulum on the pelvis virtual model (PM), and then determiningthe center of that circle. Then, the planning software may calculate thedistance of the margin as the distance between the center of that circleand the apex 202 of the planned prosthesis placement. Here, the lengthof the distal stop end 162 of the stop member 156 and the tool centerpoint 158 may not necessarily be known, nor may the position of theproximal stop end 172 of the instrument holder 118 be known in therobotic system coordinates. In another inventive embodiment, thecomputing system 104 can calculate the length of the margin if: a) thelength between the distal stop end 162 of the stop member 156 and thetool center point 158 is known in the computing system 104; b) theproximal stop end 172 of the instrument holder 118 is known andprogrammed as a link in the kinematic chain of the robot; and c) thedesired depth is known in the robotic or tracking system coordinatesystem from registration. After the length of the margin is determined,the instrument holder 118 is translated, manually or automatically,along the desired axis 204 in a distal direction towards the pelvis (P),with the grater 155 still resting on the acetabulum, by the determineddistance of the margin. The instrument holder 118 is then rigidly heldat this location during the reaming process. As the user reams theacetabulum and translates the reamer 120′ towards the desired depth, thedistance between the distal stop end and proximal stop end 172decreases. Once the user reaches the desired depth, the proximal stopend 172 of the instrument holder 118 makes contact with the distal stopend 162 of the stop member 156 or in contact with the distal stop end ofhandle 160, thereby physically stopping the user from over-reaming theacetabulum.

With reference to FIG. 4, another inventive embodiment of a method forcontrolling the depth of the reamer 120′ with the axes ‘L’ and 204aligned includes a step-wise advancement of the reamer 120″ toward thedesired depth facilitated by the surgical robot 102. First, the surgicalrobot 102 aligns the axes ‘L’ and 204 and positions the instrumentholder 118 at a position proximal to the bone. A user then translatesthe reamer 120″ towards the bone to engage the stop member 156 with theinstrument holder 118. The user may then digitize the tool center point158 to determine the distance between the tool center point 158 and theinstrument holder 118. In other inventive embodiments, the distancebetween the tool center point 158 and distal portion 162 of the stopmember 156 is already known and stored in the computing system 104.Subsequently, the user hand-guides the instrument holder 118, with thestop member 156 and instrument holder 118 engaged, until the gratermakes contact or fits into the acetabulum at a position as desired bythe user (e.g., a starting reaming position). The user then signals tothe computing system 104 that the reamer is at a starting position. Now,because the distance between the instrument holder 118 and tool centerpoint 158 is known, the distance between the tool center point 158 andthe desired depth is also known from the registration. The surgicalrobot 102 may then advance, step-wise, the instrument holder 118 towardsthe desired depth. The user may signal to the computing system 104 whento advance to the next step, wherein the surgical robot 102 thenadvances the instrument holder 118 by an ‘x’ distance (e.g., 1 mm, 2 mm,N mm). The instrument holder 118 and stop member 156 stay engagedthroughout the advancement process. The user then has the ability toadvance the instrument holder 118 in between reamer 120″ changes. Oncethe reamers 120″ reaches the desired depth, the surgical robot 102ceases to advance, or alerts the user that the desired depth has beenreached. In specific inventive embodiments, the computing system 104 mayhave an override feature that permits the user to continue reamingbeyond the desired depth.

With reference to FIG. 6, in a particular inventive embodiment, theinstrument 120′″ and/or the instrument holder 118 may include one ormore suppression elements 176 such as a force suppressing springs orelastic padding. The suppression element 176 is configured to dampen orsuppress excessive forces that may be transferred to the manipulator arm112 when the instrument 120′″ makes contact with the instrument holder118. In one inventive embodiment, the suppression element is positionedat the proximal end 172 of the instrument assembly portion 170. Inanother inventive embodiment, the suppression element 176 (shown indoted lines) may be positioned at distal end 162 of the stop member 156.In a further inventive embodiment, suppression elements 176 arepositioned at both locations. Therefore, the components (e.g., motors,encoders) of the manipulator arm 112 are not harmed while the userimpacts or reams the acetabulum, especially as the user approaches thedesired depth. It should be appreciated however, that if suppressionelements 176 are present, then a proximal end 178 of the suppressionelement 176 must now act as the proximal end 172 of the instrumentassembly portion 170 to make many of the aforementioned methods work.Likewise, if a suppression element 176 is positioned on the instrument,then a distal end of the suppression element 176 must now act as thedistal end 162 of the stop member 156. In another inventive embodiment,the forces may be suppressed on the manipulator arm using a magneticholder assembly as described in co-pending U.S. Prov. Pat. Ser. No.62/420,064.

Sensor Based Intraoperative Depth Control

In a particular inventive embodiment, with reference to FIG. 7, theinstrument holder 118 may include one or more depth sensors 180 tomonitor and control the depth of the reamer 120″. In one inventiveembodiment, the depth sensor 180 is a linear variable differentialtransformer (LVDT). The LVDT may sense the displacement of the shaft 152of the reamer 120″ while the user is reaming. The shaft 152 of thereamer 120″ may include core positioned a known distance from the toolcenter point 158. The surgical robot 102 may then position theinstrument holder 118 having the LVDT proximal to the bone such that theLVDT can interact with the core and measure the displacement of thereamer 120′ as the user reams the acetabulum. Once the user reaches thedesired depth, the computing system 104 may alert the user that thedesired depth has been reached.

In another inventive embodiment, the depth sensor 180 is a linearencoder. The shaft 152 of the reamer 120″ may include a plurality ofindentations or markings readable 182 by the linear encoder. Thesurgical robot 102 may then position the instrument holder 118 havingthe linear encoder proximal to the bone such that the linear encoder mayread the markings and measure the displacement of the reamer 120″ as theuser reams the acetabulum. Once the user reaches the desired depth, thecomputing system 104 may alert the user that the desired depth has beenreached.

OTHER EMBODIMENTS

While at least one exemplary inventive embodiment has been presented inthe foregoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary inventive embodiment or exemplary inventive embodiments areonly examples, and are not intended to limit the scope, applicability,or configuration of the described inventive embodiments in any way.Rather, the foregoing detailed description will provide those skilled inthe art with a convenient roadmap for implementing the exemplaryinventive embodiment or exemplary inventive embodiments. It should beunderstood that various changes may be made in the function andarrangement of elements without departing from the scope as set forth inthe appended claims and the legal equivalents thereof.

1. A method to guide a user in preparing a bone of a subject to receivea prosthesis to a desired depth utilizing a robotic surgical systemhaving a manipulator arm, an instrument holder attached to themanipulator arm, and surgical planning data designating a desired axisand depth to implant the prosthesis in the bone, the method comprising:providing an instrument having a shaft having a working end and a stopmember proximal to the working end; assembling the shaft to theinstrument holder between the working end and the stop member where theshaft is free to translate along a longitudinal axis of the instrumentrelative to the instrument holder; registering the surgical planningdata to the bone to determine intra-operative coordinates of the desiredaxis and depth; and positioning the instrument holder at a positionproximal to the bone such that the stop member contacts the instrumentholder to prevent the instrument from being translated beyond thedesired depth.
 2. The method of claim 1 wherein the bone is anacetabulum.
 3. The method of claim 2 wherein the instrument is a reameror an impactor.
 4. The method of claim 3 wherein the reamer or impactorfurther comprises a handle.
 5. The method of claim 4 wherein the stopmember is the handle.
 6. The method of claim 3 further comprising,reaming, with the reamer, the acetabulum to the desired depth.
 7. Themethod of claim 3 further comprising, impacting, with the impactor, theprosthesis to the desired depth.
 8. The method of claim 1 furthercomprising protecting the manipulator arm while using the instrument. 9.The method of claim 8 wherein the protecting is by adding one or moreforce suppressing springs or elastic padding to the stop member or aproximal end of the instrument holder.
 10. (canceled)
 11. A method toguide a user in preparing a bone of a subject to receive a prosthesis toa desired depth utilizing a robotic surgical system having a manipulatorarm, an instrument holder attached to the manipulator arm, and surgicalplanning data designating a desired axis and depth to implant theprosthesis in the bone, the method comprising: providing an instrumenthaving a shaft having a working end and a stop member proximal to theworking end; assembling the shaft to the instrument holder between theworking end and the stop member where the shaft is free to translatealong a longitudinal axis of the instrument relative to the instrumentholder; registering the surgical planning data to the bone to determineintra-operative coordinates of the desired axis; manipulating the arm tothe desired axis so the longitudinal axis of the instrument aligns withthe desired axis; resting the working end on an outer surface of thebone to define a linear separation between the working end resting on asurface of the bone and the desired depth to implant the prosthesis;proximally translating the instrument holder to contact the stop member;and distally translating the instrument holder along the shaft by adistance corresponding the linear separation such that the stop membercontacts the instrument holder to physically stop the instrument frombeing translated beyond the desired depth.
 12. (canceled)
 13. Animproved method of guiding a user in preparing a bone of a subject toreceive a prosthesis to a desired depth utilizing a robotic surgicalsystem having a manipulator arm, an instrument holder attached to themanipulator arm, and surgical planning data designating a desired axisand depth to implant the prosthesis in the bone, by providing aninstrument having a shaft having a working end and a stop memberproximal to the working end; assembling the shaft to the instrumentholder between the working end and the stop member where the shaft isfree to translate along a longitudinal axis of the instrument relativeto the instrument holder; registering the surgical planning data to thebone to determine intra-operative coordinates of the desired axis;manipulating the arm to the desired axis so the longitudinal axis of theinstrument aligns with the desired axis, wherein the improvement liesin: positioning the instrument holder at a position proximal to the bonesuch that the stop member contacts the instrument holder to prevent theinstrument from being translated beyond the desired depth, or distallytranslating the instrument holder along the shaft by a distancecorresponding to a linear separation between the working end resting onthe surface of the bone and the desired depth to implant the prosthesiswherein the stop member will contact the instrument holder to physicallystop the instrument from being translated beyond the desired depth. 14.The method of claim 11 wherein the shaft is adapted to attach to aninstrument holder of a surgical robot between the working end and thestop member where the shaft is free to translate along a longitudinalaxis of the instrument relative to the instrument holder, wherein theinstrument holder is at a position proximal to the bone such that thestop member will contact the instrument holder to prevent the instrumentfrom being translated beyond the desired depth.
 15. The method of claim14 wherein the instrument further comprises a handle.
 16. The method ofclaim 15 wherein the stop member is the handle.
 17. The method of claim14 wherein the stop member further comprises one or more forcesuppressing springs or elastic padding.
 18. The method of claim 14wherein a proximal end of the instrument holder further comprises one ormore force suppressing springs or elastic padding.